Recently, in consideration of environmental issues, electrically powered vehicles driven by a force supplied from an electric motor, such as electric vehicle, hybrid vehicle, and fuel cell vehicle have been of interest. Such an electrically powered vehicle is mounted with a power storage device formed of a secondary battery, an electrical double layer capacitor or the like for supplying electric power to the electric motor and storing electrical energy into which kinetic energy is converted by regenerative braking.
For such a vehicle driven by a force supplied from the electric motor, it is desirable to have a greater charging/discharging capacity of the power storage device in order to enhance the acceleration performance and the travel performance such as mileage per charge. Accordingly, as a method for increasing the charging/discharging capacity of the power storage device, a configuration mounted with multiple power storage devices has been proposed. For example, Japanese Patent Laying-Open No. 6-276609 (Patent Literature 1) discloses an electric drive system having a plurality of (three for example) storage batteries each having a DC-to-DC converter interface between the storage battery and an inverter.
Further, Japanese Patent Laying-Open No. 2003-209969 (Patent Literature 2) discloses an electrical motor power management system providing a desired DC high voltage level to a high voltage vehicle traction system. This electrical motor power management system includes a plurality of power supply stages each having a battery and a boost/buck DC-to-DC converter and connected in parallel for supplying DC power to at least one inverter, and a controller controlling a plurality of power supply stages so that batteries of a plurality of power supply stages are equally charged and a plurality of power supply stages maintain a battery voltage to at least one inverter.